Up until now, there has been proposed an exhaust gas recirculation apparatus for recirculating exhaust gas burned in a combustion chamber to an intake passage as an EGR gas to reduce a fuel consumption amount of an internal combustion engine (see for example Patent Document 1).
The exhaust gas recirculation apparatus disclosed in the Patent Document 1 comprises an EGR passage for allowing part of the exhaust gas flowing in an exhaust passage to be recirculated to an intake passage, an EGR valve provided in the EGR passage to adjust the flow amount of the EGR gas to be recirculated in the intake passage, and an EGR cooler provided between the EGR valve and the exhaust passage to cool the EGR gas by heat exchange between the EGR gas and cooling water to be used for the internal combustion engine.
The exhaust gas recirculation apparatus thus constructed can realize the recirculation of the EGR gas to the intake passage from the exhaust passage in response to the operation state of the internal combustion engine by adjusting the flow amount of the EGR gas to be recirculated in the EGR passage by the EGR valve.
The EGR gas contains PM (particulate matter), unburned gas, lubrication oil, and the like, which are adhered to or accumulated on a valve body or a valve seat forming part of the EGR valve. These foreign matters caught between the valve body and valve seat hinders the valve body from being seated on the valve seat, thereby causing a trouble that the circulation flow amount of the EGR gas cannot be controlled.
For this reason, the EGR valve is constituted by a flow control valve such as a poppet-type valve or a butterfly-type valve which is capable of selectively opening or closing the EGR passage.
There are known, as conventional exhaust gas recirculation apparatuses, such apparatuses capable of adjusting the opening degree of the valve by moving the valve body upward and downward by a stepping motor. (For example, Patent Document 2)
The exhaust gas recirculation apparatus disclosed in the Patent Document 2 comprises an exhaust gas recirculation passage for communicating the exhaust passage and the intake passage of the internal combustion engine, an exhaust gas recirculation control valve arranged in the exhaust gas recirculation passage to have the opening degree of the valve body with respect to the valve seat designed to be controlled by the reciprocating motion of the valve body activated by a motor, and a foreign matter removal control unit for performing a foreign matter removal operation to open the valve body to the fully opened position at least once in the event that predetermined conditions are established. Here, the aforementioned predetermined conditions include a condition to be established before the start of the cranking at the time of the start of the internal combustion engine.
By the construction set forth in the above description, the foreign mater removal operation is performed at the start of the internal combustion engine but not immediately after the stop of the internal combustion engine as the time of the predetermined condition fully achieved. Therefore, the oil component with a viscosity that may cause the foreign matters to be adhered is evaporated to some extent, and the valve body is fully opened with the foreign matters maintained in dry conditions, thereby making it possible to easily remove the foreign matters caught between the valve body and the valve seat. In addition, the influence to the operability of the engine can be lowered because the opening and closing operations of the valve body are performed before the start of the internal combustion engine.
Further, in recent years, to improve the control of EGR gas in the low flow area, butterfly-type valves are being adopted in lieu of poppet-type valves (see for example Patent Document 3).
The control apparatus of the internal combustion engine as disclosed in the Patent Document 3 is applied to an internal combustion engine which comprises a butterfly valve body arranged in the gas passage of the internal combustion engine, and an actuator to rotate the butterfly valve body, so that the actuator is operated to perform the control to open and close the butterfly valve body. The control apparatus of the internal combustion engine as disclosed in the Patent Document 3 comprises a deposit amount estimation unit operative to calculate the amount of the deposits generated in response to the operation state of the internal combustion engine and to estimate the amount of the deposits accumulated in the gas passage by summing up the amount of the deposits thus calculated, and a deposit removal unit operative to rotate the butterfly valve body based on the accumulated amount of the deposits estimated by the deposit amount estimation unit to remove the deposits at the time of the operation of the internal combustion engine.
The control apparatus of the internal combustion engine as disclosed in the Patent Document 3 is operative to remove the accumulated deposits during the operation of the internal combustion engine, thereby making it possible to effectively remove the deposits. To be more specific, the control apparatus of the internal combustion engine is so designed to rotate the butterfly valve body during the operation of the internal combustion engine when there is generated the flow of the gas in the gas passage, so that the deposits caught in the butterfly valve body are blown off by the flow of the gas, thereby making it possible to effectively remove the deposits.